1. Field of the Invention
This invention relates to the endless fabric belts used on papermaking machines to support, carry, and dewater the wet fibrous sheet as it is being processed into paper. It more specifically relates to seamed, rather than endless, fabrics, and to the pintles used to close the seam formed when the two ends of the fabric are joined during installation on the machine.
2. Description of the Prior Art
Endless fabric belts are key components of all three sections (forming, pressing, and drying) of the machines used to manufacture paper products. There, like a conveyor belt, they carry the wet fibrous sheet along as it is being converted into a paper product. At the same time, they provide needed support to the fragile, wet paper sheet and dewater it by accepting water which drains or is pressed therefrom.
Generally, these fabrics are supplied either in endless form, that is, woven in the form of an endless loop without a seam, or in open-ended form. The latter must be closed into endless form when installed on the papermachine. This will leave a seam running transversely across the fabric at the point where the two ends meet.
The so-called OMS (on-machine-seamed) fabrics are much easier to install on a papermachine position than those of the woven endless variety. To do so, one merely has to draw one end of the open-ended fabric through the machine and around the appropriate guide and tension rolls and other components. Then, the two ends can be joined at a convenient location on the machine and the tension adjusted to make the fabric taut. In practice, a new fabric is installed at the time an old one is being removed by connecting one end of the new fabric to the old fabric, which is used to pull the new fabric into proper position on the machine.
By way of contrast, the installation of an endless fabric is a much more difficult and time-consuming undertaking. The machine must, of course, be shut down and the old fabric cut out or otherwise removed. The new fabric must then be slipped into the machine from the side through spaces in the frame and around various machine components. This difficult job is compounded by the fact that the newer fabrics have been becoming increasingly bulkier and stiffer. This increases the time and effort necessary on the part of plant personnel to install a new one. Viewed in this light, the development of OMS fabrics has been a great boon.
The formation of the seam will be our primarily concern here. While there are a number of forms of such seams, we will be specifically interested in that known as the pin seam. This form of seam is more difficult to distinguish from the rest of the body of the fabric than those formed in other ways.
To close a pin seam, a thin cable, better known as a pintle, is passed down through the tunnel formed by the loops at each end of the fabric, when the two ends are brought together in such a way that the loops alternate and intermesh. The loops themselves are formed in one of two ways. In the first way, they are formed by the machine-direction yarns themselves, looped and woven back into the fabric. The second way employs a modification of the art of weaving "endless", which normally results in a continuous loop of fabric. According to the modification, the edges of the fabric are woven in such a way that the body yarns form loops, one set of alternating loops for each end of the woven cloth. In each way, the seam location will be nearly the same thickness as the rest of the fabric.
While the seam location might be of approximately the same thickness as the rest of the fabric, it most likely will not have the same physical properties. Specifically, it can turn out to have greater or lower permeability to air and water than the rest of the fabric depending upon the fit of the pintle, the permeability of the pintle itself, and any gap in the seam region In addition, under compression the seam region may behave differently than the rest of the fabric. The end result of these problems will be the periodic marking of the paper sheet by the seam. Although for some paper grades, and contemplated end uses, this may not be a serious problem, marking in general is undesirable.
Unfortunately, there is no ideal pintle. The present invention, however, provides a pintle having a cross section of novel shape, designed to reduce the marking of the paper sheet by the seam.